On Wed, 2 Dec 2009 06:01:43 -0800 (PST), "
wrote:

On Dec 2, 5:01*am, Ned Simmons wrote:

Well, thanks for sticking with me on this. It may not have much
practical value -- I'm not planning on installing $300 bearings where
$8 units will do, but it's good exercise.

Now back to the birthers...

--
Ned Simmons

It may not have any value at all. The $8 bearing has a minimum
tolerance. There is no guarantee that it will have characteristics
that Ed says will make it last longer in a poor mounting. The $300
bearings are selected after manufacture from the lot that has the $8
bearings.

That may be true of resistors, but not bearings. For example, Barden
makes *only* precision bearings. Precision bearings also have
different cages than the bearing you get if you simply ask for a 6206.

So if the demand for $300 bearings isn't very high, you may
get a high precision bearing from the $8 bin. Also bearing
manufacturing has improved in the last thirty years. So more of the
$8 bearings are closer to meeting the specs of the $300 bearings.

Granted not all manufacturers have tighter control on their
production.

This is true. I was told by an SKF engineer that most of their ABEC 1
deep row bearings will meet ABEC 5 standards, and I've verified this
in a couple cases where I built very low speed spindles with sub-tenth
runout using ABEC 1 bearings. The fallback plan was to replace the
bearings with precision units, but it wasn't necessary.

--
Ned Simmons